In an application entitled "Intra-Vaginal Device and Method," Ser. No. 348,204, filed Apr. 5, 1973 now U.S. Pat. No. 3,854,476, incorporated herein by reference, an intra-vaginal contraceptive device is described which includes an elongate member with a disc disposed to the posterior end flexibly coupled to an extension element at the anterior end of the device. The illustrated extension element includes a flexible frusto-conical portion. The length of the overall device and the diameter of the frusto-conical portion vary depending upon the size of the animal's vaginal tract. Because of the size and shape of the disc which assists retention of the device, it would be time consuming and irritating to the animal to make size measurements by trial and error insertions of contraceptive devices of varying sizes. Thus, there is a need for a measuring device which accurately determines the appropriate size of the frusto-conical portion of the contraceptive device in a relatively short period of time without these disadvantages.